To satisy requirements of modem telecommunication systems, designers and manufacturers of optical components are facing an increasing need for more complex optical components, designed to combine higher numbers of functions and channels in a single device. The integration of optical and electrical components into a single device became a major milestone of opto-electrical component design. Analogous to the integration of functions in electrical Integrated Circuits (ICs) opto-electronic functions are now integrated in Photonic Integrated Circuits (PICs). Use of semiconductor compounds such as InGaAsP/InP and GaAlAs/GaAs—having bandgaps corresponding to a wavelength range used in Wavelength Division Multiplexing (WDM) networks—allow integration of active and passive functions on a same semiconductor chip.
However, these anisotropic semiconductor compounds exhibit a relative permittivity —or dielectric constant—that varies as a function of the orientation of the electrical field of the Transverse Electro-Magnetic (TEM) wave traveling therethrough, making them highly polarization dependent, or birefringent. Modern design of PICs has to take into account this material property. The stochastic nature of the State of Polarization (SoP) of different WDM optical signals in an optical communication system necessitates design and manufacture of polarization-insensitive or polarization-compensated PICs.
High-level integration of passive and active functionalities found in state of the art PICs has forced the development of new testing and analysis strategies. U.S. Pat. No. 5,371,597 issued Dec. 06, 1994 to Favin et al. teaches a measurement technique to extract Mueller matrix terms of a Device Under Test (DUT) to provide Polarization Dependent Loss (PDL) spectra over a large wavelength range. However, the inherent birefringence resulting from overall boundary condition solution of multiple epitaxial layers needs to be carefully compensated to yield polarization insensitive PICs. To this end, a Polarization Dependent Frequency (PDf) shift—which corresponds to the birefringence-induced centre frequency variations—needs to be determined. This is achieved by determining the incident optical spectrum of the two extreme orthogonal SoPs, referred to as Transverse Electrical (TE) or horizontal electrical field and Transverse Magnetic (TM) or vertical electrical field modes. U.S. Pat. No. 6,762,829 issued Jul. 13, 2004 to Babin et al. teaches a technique based on a conventional use of Mueller calculus involving sampling of a large number of incident SoPs, where each SoP represents a point on the Poincaré sphere. For each of these points an output insertion loss spectrum or a responsivity spectrum is simulated. From the simulated spectra, specific parameters such as centre frequency and filter bandwidth are evaluated. However, this technique requires substantial computational efforts, is very time consuming and, therefore, is not suitable for testing PICs in a manufacturing process. Furthermore, this technique does not ensure orthogonality of the incident two extreme orthogonal SoPs.
It would be desirable to provide a method and system for determining polarization dependent characteristics based on Mueller matrix terms ensuring orthogonality of the incident two extreme SoPs. It would be further desirable to substantially reduce the computational effort needed to determine the polarization dependent characteristics, thus allowing volume testing based on Mueller matrix terms in a manufacturing process.